Objective Synovitis and tenosynovitis are present in juvenile idiopathic arthritis (JIA), both as joint pain and/or inflammation, making them difficult to detect on physical examination. Although ultrasonography (US) allows for discrimination of the 2 entities, only definitions and scoring of synovitis in children have been established. This study was undertaken to produce consensus‐based US definitions of tenosynovitis in JIA. Methods A systematic literature search was performed. Selection criteria included studies focused on US definition and scoring systems for tenosynovitis in children, as well as US metric properties. Through a 2‐step Delphi process, a panel of international US experts developed definitions for tenosynovitis components (step 1) and validated them by testing their applicability on US images of tenosynovitis in several age groups (step 2). A 5‐point Likert scale was used to rate the level of agreement. Results A total of 14 studies were identified. Most used the US definitions developed for adults to define tenosynovitis in children. Construct validity was reported in 86% of articles using physical examination as a comparator. Few studies reported US reliability and responsiveness in JIA. In step 1, experts reached a strong group agreement (>86%) by applying adult definitions in children after one round. After 4 rounds of step 2, the final definitions were validated on all tendons and at all locations, except for biceps tenosynovitis in children <4 years old. Conclusion The study shows that the definition of tenosynovitis used in adults is applicable to children with minimal modifications agreed upon through a Delphi process. Further studies are required to confirm our results.